Idle drops when sub hits, alternator to blame?

I am wondering if it is a sign that my bettery or alternator is going out becasue I can watch my idle drop 100-150 RPM when the sub hits when the volume is loud, it doesnt do it if I turn it down, and it gets worse the more I turn it up.

Is somthing wrong or do I just need to suck it up and get a cap?


apparently its normal that it happens if you dont have a stablizer for the sub its draining quite some power from there. I had similar problem with idle going down when electricals were in use. I just changed the battery for about ~$40. not much especially if your battery is hella old. I dunno bout the alternator. Shouldnt be the alternator. Read my other thread in this section about my idling rpm. It just needs some cleaning and maybe some tune up.

common problem with systems in cars with smal batteries… get a farad capacitor and it should help quite abit with the problem, if it goes on to long could drain battery if cars off.


Would it be better to get a cap or a optima yellow top? Im probably going to have to sell all my sound stuff before I hed off to school, no use it sitting 9 months out of the year :frowning:

System Setup

Just going to list what I have in my car and I don’t get a idle drop. I have 2 Phoenix Gold 180Watt AMP’s pushing 2 Phoenix Gold 200Watt 10’s. A 1 farad Cap and a red top optima bettery. I have more stuff but you get the idea from that. I would recommend getting a 1/2 or 1 farad cap and/or a optima red top bettery. I would have got a yellow but I dont wanna mess around with taking out the black thing that holds the battery. I got my battery at Auto Zone to replace my old one and it was around $113 after tax. They had 2 red tops on bigger then the other but the smaller one fits in without any trouble (just so you know). If anyone wants a list of excatly what I have just drop me a line.

You can damage your battery and/or altanator if you do not get a cap or bettery battery. I know I had this system in a old accord and it killed both my battery and alt which was no fun changing since it was back by the firewall on the lower half of the engine.

In the trunk I have a Phoenix Gold Xeon 400.1 to a JL 10" w3v2. Sucks a lot of power lol.

So I guess ill look into a cap…Thanks

I do have somthing to add though. I guess people are telling me that it could be fixed by a better battery or a cap, well my battery is a 630 amps at 32 F, and I started it once this winter up in the mountains when it was -5 F outside, and it started just fine, didnt sound weak or anything. So I think my battery is fine, but a yellow top is $110 and a 1 F cap is $55

Im just wondering if that bettery may be ok but just needs a cap with it.



I would say get a cap. That AMP does pull alot of power. Just because you think your battery is good it doesnt mean that it can haldnt everything in your car and AMP running. I would get an AMP and see if that helps.

standard car batteries are not made to supply large jolts of power, like those drawn when the sub hits. that is where a cap helps, caps are made to dump power quickly (camera flash, for example).

The yellowtop allows the battery to be discharged more without damage. Not sure it would help you any with sub power draws.

Alright, im off to grab a phoenix gold 1 F cap tommarow :smiley:

Hopfully that will help

please don’t be surprise that when you install your cap that your lights or idle problem will go away make sure your battery is fully charged and you do have a good battery :rockon:

Ok i bought a stinger 1F cap off sounddomain… 10 bucks cheaper, almost as good and has the cool led readout :wink: Hope it helps :frowning:

Some possible things that might help.
Upgrade the power wire from the alt. to the battery.
Upgrade the ground wires.

Hmm never thought about the wire from the alt to the batt. Ill have to take a look, maybe throw some 2 G on there, since the wire from the batt to the amp is 4G :smiley: